1. Field of the Invention
The present invention relates to an image coding apparatus and image coding method, image decoding apparatus, and recording medium, and more particularly relates to the image coding apparatus and image coding method, image decoding apparatus, image transmitting method and recording medium capable of thinning-out (sub-sampling) and compressing an image in such a manner as to obtain a decoded image almost identical to the original image.
2. Description of the Related Art
Conventionally, various methods have been put forward as methods for compressing images, with one of these methods being a method for compressing images by thinning-out the number of pixels.
However, when an image compressed by this kind of thinning-out is simply expanded by interpolation, the resolution of the resulting decoded image is poor.
There are two reasons for this kind of deterioration in the resolution of the decoded image. One reason is that high frequency components included in the original image are not included in the thinned-out image. A second reason is that the pixel values for pixels comprising images after thinning-out are not particularly suitable for decoding the original image. Accordingly, it would be desirable to provide methods and apparatus which resolves such problems.
As the present invention sets out to resolve these problems, the present invention is capable of thinning-out (subsampling) and compressing images in such a manner that decoded images that are identical (almost identical) to the original images can be obtained.
According to one aspect of the present invention, an image coding apparatus includes correction means which corrects compressed data obtained by compressing the original image data to a fewer number of pixels and outputs corrected data. Prediction means predicts the original image based on the corrected data and outputs the predicted value. An arithmetic means calculates a prediction error for the predicted value with respect to the original image data. Determining means determines suitability of the corrected data outputted by the correction means based on the prediction error. Outputting means outputs the corrected data as the original image data coding results in accordance with determination results of the determining means.
According to another aspect of the present invention, an image coding method compresses an original image data to a fewer number of pixels by correcting compressed data obtained by compressing the original image data and outputting corrected data, predicting the original image data based on the corrected data and outputting a predicted value and calculating a prediction error for the predicted value with respect to the original image data is repeatedly carried out until the prediction error becomes less than a prescribed threshold value, and the corrected data is then outputted as coding results for the original image data.
According to yet another aspect of the present invention, in an image decoding apparatus, coded data decoded by the decoding means is obtained when the prediction error becomes less than a prescribed threshold value as corrected data by repeatedly compressing an original image data to a fewer number of pixels, correcting compressed data obtained by compressing the original image data and outputting corrected data, predicting the original image data based on the corrected data and outputting a predicted value; and calculating a prediction error for the predicted value with respect to the original image data until the prediction error becomes less than a prescribed threshold value.
According to a further aspect of the present invention, a recording medium is recorded with corrected data when a prediction error is less than a prescribed value, obtained by repeatedly correcting compressed data obtained by compressing the original image data to a fewer number of pixels and outputting corrected data, predicting the original image data based on the corrected data and outputting a predicted value and calculating a prediction error for the predicted value with respect to the original image data until the prediction error becomes less than a prescribed threshold value.
According to another aspect of the present invention, the image coding apparatus includes prediction means having adaptive processing means for carrying out adaptive processing for obtaining predictive coefficient for each class for calculating said predicted values using a linear combination with the corrected data so as to obtain the predicted value based on this predictive coefficient.
According to yet another aspect of the present invention, the image coding apparatus includes prediction means having sorting means for sorting the corrected data into prescribed classes in response to characteristics of the corrected data and the adaptive processing means carries out adaptive processing each the prescribed class.
According to a further aspect of the present invention, the image coding apparatus includes transmitting means for transmitting the corrected data outputted by the outputting means.
According to an aspect of the present invention, the image decoding apparatus is an image coding apparatus for decoding data coded for an image, which includes decoding means for decoding the coded data, the coded data being corrected data when a prediction error is less than a prescribed value, obtained by repeatedly compressing an original image data to a fewer number of pixels, correcting compressed data obtained by compressing the original image data and outputting corrected data, predicting the original image data based on the corrected data and outputting a predicted value and calculating an estimation error for the predicted value with respect to the original image data until the prediction error becomes less than a prescribed threshold value.
These and other aspects of the invention will become apparent when considered with reference to the following description and the accompanying drawings.